Heptasartorite is an extremely rare thallium-lead sulfosalt found almost exclusively in the famous Lengenbach Quarry in Switzerland. It typically occurs as small, lead-grey, heavily striated prismatic crystals associated with other complex sulfosalts in dolomite. Due to its extreme rarity and toxicity, it is sought primarily by advanced systematic mineral collectors.

Hardness

3-3.5

Mohs

Luster

Metallic

Streak

Dark brown

Transparency

Opaque

mineralrareSartorite Group family

Heptasartorite

Hardness: 3-3.5
Luster: Metallic
Streak: Dark brown
Transparency: Opaque

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Is this heptasartorite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch heptasartorite with a known reference. Heptasartorite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: dark brown.
3
Read the luster
Hold the specimen under a strong light. Luster: metallic.
4
Match the color range
Compare against the expected color range: lead-gray.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: striated prismatic crystals.

Often confused with

Heptasartorite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Sartorite

Mohs 3

How to tell apart: Streak differs, so Heptasartorite leaves dark brown, Sartorite leaves chocolate-brown.

How to tell apart: Streak differs, so Heptasartorite leaves dark brown, Gratonite leaves black.

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Often found alongside heptasartorite

Minerals reported to co-occur with heptasartorite. Spotting these in float or country rock is a strong cue you are in the right ground.

Enneasartorite
mineral · Mohs 3-3.5

All properties

Chemical formula: Tl₇Pb₂₂As₅₅S₁₀₈
Mohs hardness: 3-3.5
Density: 4.9 g/cm³
Colors: Lead-gray
Streak: Dark brown
Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Striated prismatic crystals
Cleavage: Good on {100}
Rarity: Rare
Uses: Collector
Host rock: In dolostone

Where rockhounds find heptasartorite

Classic worldwide localities

Lengenbach quarry, Binntal, Wallis, Switzerland

Field-hunting tip

Where it forms: In dolostone. If you start seeing enneasartorite in float, you are in the right ground. Typical habit: striated prismatic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify heptasartorite?+

Mohs hardness is 3-3.5. Luster: metallic. The streak is dark brown. Common colors include lead-gray.

Where is heptasartorite found?+

Notable localities include Lengenbach quarry, Binntal, Wallis, Switzerland.

Is heptasartorite safe to handle?+

Heptasartorite contains arsenic, lead and thallium and calls for real care. Contains thallium and arsenic; handle with gloves, avoid inhaling dust or ingesting particles, and wash hands thoroughly after handling.

What rocks look like heptasartorite?+

Heptasartorite is most often confused with Sartorite, Gratonite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with heptasartorite?+

Heptasartorite commonly co-occurs with Enneasartorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does heptasartorite form in?+

Where it forms: In dolostone. Working float back to the host body is the standard way to chase a fresh occurrence.

What is heptasartorite used for?+

Heptasartorite is used in collector.

Find heptasartorite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.